An organism's ability to learn is a fundamental aspect of how motor behaviors become adaptive to the environment. The investigators have become particularly interested in understanding mechanisms that underlie a form of associative learning, the classically conditioned eye blink reflex. In behaving animals, this response consists of eyelid closure following an airpuff to the cornea. When an auditory stimulus is paired with the airpuff, the animal learns to close the eyelid in response to the auditory stimulus alone. Previous studies of these researchers have demonstrated that a neural correlate of an eye blink reflex can be classically conditioned entirely in vitro. Data suggest that activity recorded in the abducens nerve, which contains motoneuronal projections to the extraocular muscles, can be conditioned by pairing a trigeminal nerve unconditioned stimulus (US) with an auditory nerve conditioned stimulus (CS). This classically conditioned abducens nerve response shows gradual acquisition to paired stimuli, and extinction when the stimuli are unpaired. Acquisition is rapid, taking place in about two to three hours. Using this in vivo classically conditioned eye blink reflex model, the proposed studies will be directed at understanding the synaptic mechanisms that underlie this form of motor learning with the larger aim of elucidating how behaviors become adapted to environmental demands. The Specific Aims will address the following issues related to mechanisms underlying in vitro classical conditioning: 1) To assess the distribution of glutamate receptor subunits during classical conditioning by using immunocytochemistry and light microscopy; 2) To examine the levels of glutamate receptor proteins before and after conditioning by using western blot analysis; 3) To obtain intracellular recordings from abducens motoneurons to assess the pharmacological basis (AMPA and/or NMDA) of synaptic potentials from nerves conveying the CS and US, and 4) to perform intracellular recordings to examine changes in synaptic potentials during conditioning and pharmacological manipulation of cellular mechanisms.